A bit of background for this topic: Alembic is not a single file format, it can be stored in two different ways: Ogawa and HDF5. Ogawa replaced HDF5 and is smaller and much faster (4-25x) to read (source).
As long as Blender has had Alembic support, it has never supported the HDF5 format in any release. There is a build-time option
WITH_ALEMBIC_HDF5 that can be used to enable HDF5 support in your own build, though. In the years that I have been maintainer of Blender’s Alembic code, I’ve seen very little requests to enable HDF5 support in an official release. As a matter of fact, I only remember getting such a request once, and that was to support very old software. After I suggested to check whether that software had an update I never heard back, so I guess they also upgraded to Ogawa.
Now that I’m working on improvements to the Alembic exporter, I’m once again seeing the
#ifdef WITH_ALEMBIC_HDF5 conditionals in the source code, and I want to get rid of this. IMO we should either properly support HDF5 or remove it altogether and clean up the code. Seeing how Ogawa is superior in every way, and how little requests for HDF5 I’m aware of, I would say let’s remove it.
Are their people or studios who build Blender for themselves and enable HDF5 support? Who would feel any impact from complete removal of HDF5 from Blender?